Air-laid absorbent sheet products are known in the art. U.S. Pat. No. 4,437,917 to Tao et al. describes a method for increasing the caliper and bulk of air-laid dry fibrous webs. The method generally includes measuring the downstream caliper of the bond curing drier and adjusting drier conditions on the basis of the caliper measurements.
U.S. Pat. No. 4,482,308 to Johnson teaches an apparatus for depositing dry fibers on a foraminous support including offset suction and air deflecting means for imparting a horizontal velocity to the fibers in the direction of the moving wire. The patent reports more uniform distribution of fibers in the product.
U.S. Pat. No. 4,476,078 to Tao describes that air-laid products are conventionally embossed either before or after the binder is applied and cured; each method having its advantages and drawbacks. Pre-embossing is reported to reduce line speed, while post-embossing lacks good embossing definition (col. 1, line 58—col. 2, line 13).
U.S. Pat. No. 4,612,231 of Bouchette et al. describes a pattern for an air-laid fibrous web of enhanced absorbency. According to the '231 patent, absorption rates are increased when at least about 40 per cent of the imprinted area of the web is compressed (col. 2, lines 23-28).
Another method of increasing the absorbency of air-laid webs is disclosed in U.S. Pat. No. 5,128,082 to Makoui. The '082 patent describes making an absorbent structure by dry laying a fibrous web having incorporated therein a superabsorbent material such as poly(acrylic acid) or a salt thereof and applying a latex coating to at least one surface of the web.
Embossing cellulosic absorbent sheet products to alter their mechanical or tactile characteristics is likewise known. There is shown in U.S. Pat. 1,808,536 to Fisk a method and apparatus for embossing paper tissue and towels using an embossing roll with a wave-like pattern. The pattern on the roll has a relief height of 0.075 inches or more above the general surface of the roll (col. 2, lines 69-75). The method is reported to be particularly suitable for wet creped products prior to the web contacting the drier rolls.
U.S. Pat. No. 186,259 to Howell shows a puffed textile fabric with a wave-like design. So also U.S. Pat. No. 728,828 to Arkell shows a bidirectional wave pattern imposed on a paper structure.
U.S. Pat. No. 3,672,950 to Murphy et al. is directed to adhesively laminated crepe products wherein the plies are bonded in superposed relation by an adhesive disposed between the webs (col. 2, lines 15-25). The adhesive may be applied in a wave-like pattern in the machine direction (FIGS. 1, 4), while the webs may be embossed with a great number of pin-like embossments. The embossments extend from the body of the web for a predetermined distance as required to keep the two webs suitably spaced, the two webs being superposed with the protuberances of each web facing the other web (col. 4, lines 29-37; col. 6, line 74—col. 7, line 1).
In U.S. Pat. No. 4,339,088 to Niedermeyer there is described an embossing method to avoid nesting in convolutedly wound rolls wherein the repeat length is at least as great as the circumference of the roll. In Example 1, a sine wave pattern of embossment nodes is laid out in the machine direction (col. 4, lines 5-35).
U.S. Pat. No. 5,861,081 of Bredendick describes a single ply-paper towel with a plurality of infundibulate bosses formed therethrough. The towel has areas of light bosses and heavy boss perforations which form islands of heavy boss perforations surrounded by intersecting bands of light bosses (col. 3, lines 33-38).
Wave-like patterns have also been employed to control fluid distribution in absorbent structures. U.S. Pat. No. Re. 29,789 to Kolbach discloses a diaper with various embossed patterns. There is disclosed, for example, an embossed roll with circumferential wave bosses (46, FIG. 1) extending the cross direction of a production line. The diapers have compressed channels 72 with a wavy line profile which functions to direct fluid in the longitudinal direction (col. 7, line 60-63; col. 8, lines 40-44).
U.S. Pat. No. 2,788,003 to Morin discloses a multi-layered diaper embossed with a wave-like pattern. The wave-like pattern is formed by embossing strips of the absorbent layer 17 against the facing sheet with a hot embossing tool. col. 3, lines 34-43. The embossed strips operate to convey fluid in the direction of the embossed lines. col. 4, lines 29-51.
U.S. Pat. No. 5,759,473 to Minke et al. describes a process for producing a silicone coated embossing roll for continuously embossing the surface of the thermoplastic film. A laser beam is used to cut into the smooth silicone rubber surface of the roll and pattern a design which replicates the negative of a leather grain. Embossed rolls described in the '473 patent are made by applying a smooth, silicone rubber coating to a steel roll. col. 2, lines 40-45.
There is described in U.S. Pat. No. 5,529,563 to Veith et al. a method of embossing between unmatched male and female embossing elements wherein one of the embossing rolls may be made of rubber. According to the '563 patent the material of the male and female embossing elements is preferably a deformable-material such as rubber, plastic and the like. See col. 3, lines 53 to col. 4, line 20 for a general description of the process.
U.S. Pat. No. 5,269,983 to Schulz describes a method of embossing involving a mated pair of resilient and rigid embossing rolls. According to the '983 patent a laser can be utilized to form recesses in a resilient roll such that the resilient roll receives protuberances of a rigid male embossing roll when the rolls are placed in contact.
U.S. Pat. No. 4,634,484 to Wagner discloses a method of producing an embossing roll for the continuous embossing of the surface of a thermoplastic film. Sheets having desired grain patterns are mounted on a roller with edges abutting. Onto the surface of the grain pattern a silicone synthetic resin is applied as a uniformly thick coating with a coating knife as the roller rotates. The resin is hardened into a matrix and then peeled off the grain pattern. The matrix is placed with the pattern outward on a roller whose diameter pretty much matches the diameter of the embossing roll to be produced. The surface of a tubular thermoplastic film is embossed by contact with a cylindrical matrix under heat and pressure. The embossed surface of the thermoplastic film is once again embossed under heat and pressure in the areas along the abutting edges of the natural grain pattern on the roller so that an endless positive impression without seams in the grain pattern is produced. Another layer of silicone rubber is applied to the positive impression which layer is vulcanized into a matrix which is peeled off the positive form and then adhered to the circumferential surface of the embossing roll with the negative side out. With this embossing roller a natural leather grain can be embossed on a thermoplastic film without the appearance of discontinuities at the abutting edges.
U.S. Pat. No. 4,917,903 to Mente discloses an apparatus for producing decorative seams on films. The method involves using a dye coated with a paste-like silicone rubber composition hardened and used to emboss a layer of plastic. See col 4, lines 49-56.
U.S. Pat. No. 2,943,560 to Wrob et al. discloses an embossing apparatus including an embossing clip with a flexible metal member to which is secured a lining of fabric and a molded embossing member preferably made of plastic, rubber or similar material. See Col. 3, lines 35-40.
U.S. Pat. No. 1,820,338 to Youngchild et al. discloses an embossing roll provided with a plurality of layers of hard rubber separated by layers of heavy fabric. The various layers are removable to expose successive hard rubber layers. See Col. 2, lines 78-83.
U.S. Pat. No. 3,425,347 to Nard discloses a printing plate including a rubber layer having an outer printing surface and an inner mating surface formed by a pattern of space uniform projections which relieve tension and provide concavity of the printing surface when a layer is mounted and adhesively secured to a curved backing roll.
U.S. Pat. No. 3,347,162 to Braznell et al. discloses rubber printing plates and a method of making them.
As can be seen from the foregoing rubber surfaces have been used for embossing, printing, and like processes. It is further noted, however, that patterned hard rubber rolls have not generally been applied to industrial processes for producing air-laid absorbent sheet where high speed, superior emboss definition, and wear considerations are paramount. In such applications steel rolls are generally still employed despite their higher manufacturing costs.
It has been found in accordance with the present invention that heated, hard rubber embossing rolls may be used to provide high quality emboss definition in air-laid webs. The inventive rolls and process of the current invention provide for more economical embossed rolls for air-laid products and also reduces the amount of time necessary to produce an embossed roll of a desired proprietary pattern.